It is customary for a gas which is as homogeneous as possible to be delivered for compression to the compressor of gas turbines. In applications where gases of different composition are available, these are first intermixed and then delivered to the compressor. For example, in the recirculation of exhaust gases, use is made of an exhaust gas which has a gas composition deviating from fresh air. Recirculation is a technology which can basically be employed for the most diverse possible purposes in gas turbines. Thus, for example, for monitoring the emissions, for reducing the exhaust gas volume for the carbon dioxide separation, etc. In the recirculation of exhaust gases in a gas turbine, an appreciable fraction of the exhaust gas is branched off from the overall exhaust gas flow and normally, after cooling and purification, is delivered again to the inlet mass flow of the turbine or to the turbine compressor. The exhaust gas composition differs considerably from the composition of fresh ambient air. It is customary for the recirculated exhaust gas flow to be intermixed with fresh air from the surroundings and for this mixture subsequently to be delivered to the compressor.
Advantageously, by exhaust gas recirculation, the carbon dioxide partial pressure in the exhaust gases can be increased in order to reduce the power losses and efficiency losses at power plants with carbon dioxide separation. What has also been proposed is exhaust gas recirculation with the aim of reducing the oxygen content in the intake gases of gas turbines in order thereby to reduce the NOx emissions.
For exhaust gas recirculation, for example, U.S. Pat. No. 7,536,252 B1 describes a method for controlling an exhaust gas recirculation flow of a turbomachine which is returned to the inlet of the turbomachine via an exhaust gas recirculation system. In this method, a desired exhaust gas recirculation fraction which contains the fraction of the exhaust gas flow in the inlet flow of the turbomachine is determined, and the actual value is set to the desired value.
EP2248999 discloses a power plant with exhaust gas recirculation and also a method for operating a power plant of this type, in that the recirculation rate and the temperature to which the recirculated exhaust gases are recooled are regulated as a function of the load.
It is typically advantageous to achieve as high a recirculation rate as possible. The recirculation rate is typically limited by the requirements of the combustion chamber, since the oxygen content of the fuel gases otherwise becomes too low and complete, CO and UHC (unburned hydrocarbon)-free combustion cannot be ensured.
In the prior art, in order to ensure good combustion when the oxygen content of the fuel gases is low, the fresh air is intermixed as thoroughly as possible with the recirculated exhaust gases in order to make available a homogeneous gas mixture at the combustion chamber inlet. A mixer suitable for intermixing fresh air with recirculated exhaust gases so as to have a low pressure loss is known, for example, from WO2010/142573 A2.
The plant parts for exhaust gas recirculation, such as the mixer, recirculation lines, cooler for the recirculated exhaust gases, etc., are large and costly and require additional space in a power plant. They also lead to pressure losses and are detrimental to the power output and efficiency of the power plant.